I have had three stones installed for a year - one on each amp and one on my Hydra. Couldn't really say they made a difference until I took a stone off the Hydra and placd it on my cd player. I had forgotten I had made this change and when I listened a few days later, the highs sounded unnatural, almost edgy. It was pretty bad - not at all how I remembered my system sounding. It was the same on vinyl, squeezebox and FM. I checked the whole system and couldn't find anything wrong, until I remembered I had moved the stone. When I placed it back on the hydra, all went back to normal. Great sound had returned. Now I know they work.
